Asia's corals in massive die-back

Emma Woollacott, 19th October 2010

The worst coral die-off in ten years - possibly ever - has struck across the Southeast Asian and Indian Oceans.

The bleaching event extends from the Seychelles in the west to Sulawesi and the Philippines in the east and includes reefs in Sri Lanka, Burma, Thailand, Malaysia, Singapore and Indonesia.

"It is certainly the worst coral die-off we have seen since 1998. It may prove to be the worst such event known to science," says Dr Andrew Baird of the ARC Centre of Excellence for Coral Reef Studies. "So far around 80 percent of Acropora colonies and 50 per cent of colonies from other species have died since the outbreak began in May this year."

Coral cover in the region could drop from an average of 50 percent to around 10 percent, and will take years to recover.

The cause of the bleaching was a large quantity of hot water which flooded into the eastern Indian Ocean a few months ago. This the corals and caused them to shed the symbiotic algae without which they starve to death.

According to the National Oceanic and Atmospheric Administration’s Coral Hotspots website, sea surface temperatures in the region peaked in late May 2010. Local dive operators recorded water temperatures of 34 C, over four degrees higher that than the long-term average.

"My colleagues and I have high confidence these successive ocean warming episodes, which exceed the normal tolerance range of warm-water corals, are driven by human-induced global warming," said Dr Baird.

"They underline that the planet is already taking heavy hits from climate change – and will continue to do so unless we can reduce carbon emissions very quickly."

Dr Baird said it won't be clear until early next year whether Australia will suffer a similar coral bleaching event. The previous worst bleaching of the Great Barrier Reef was in 1998 and 2002, when over 40 percent of its reefs were affected.